Generally, when a flash synchronizing device is provided in a camera with a multi-flash function, a constant amount of light from the flash is emitted a plurality of times, in synchronization with shutter operations. The plurality of light emissions are effected at substantially equal intervals with respect to the time base, and are independent of the size of the aperture area of the shutter. For this reason, an average flash effect is obtained. The exposure quantity is the same for all portions of the picture, however, resulting in such drawbacks that vividness is not apparent in the photographed picture, and the photo is hard to see.
Elements for determining an exposure for taking a photo are the film sensitivity, the shutter speed, the diaphragm and the brightness of a subject. If the film sensitivity and the brightness of the subject are determined, a proper exposure value can be determined. Automatic exposure (AE) control is effected by setting the shutter speed and the diaphragm value so that a proper exposure C has an exposure value based on the subject luminance E, a film ASA sensitivity S, a diaphragm value F and an exposure time T.
Under AE control, the selection by the camera of the shutter speed, the diaphragm, or all the elements depends upon the purpose of the photograph. When subjects are selected for which the depth of field must be enhanced, e.g., still-life photography, group photography (the depth of focus is needed) and a portrait (the background is out of focus while decreasing the depth), diaphragm priority AE is preferable. If the photographer sets the diaphragm value, or if, alternatively the diaphragm value is determined from a result of measuring the distance to the subject, the shutter speed is automatically set.
On the other hand, a flashmatic mechanism in which the camera interlocks with the electronic flash is a mechanism for controlling, when irradiation distance varies, the diaphragm value interlocking therewith on the basis of GN (guide number) =F.multidot.D expressed as a product of a diaphragm value indicating a light quantity of the flash and the irradiation distance D (to the subject).
For controlling the proper exposure by interlocking the flash with AE of the camera, the guide number of the flash is set, and thereafter the diaphragm is automatically adjusted simply by adjusting the distance.
The above-described flashmatic mechanism includes an auto-flashmatic mechanism constructed to emit no light when the natural light suffices for an exposure quantity of the subject but automatically emit the light under such conditions that a blur would otherwise caused due to an ambient darkness.
When the photographer selects diaphragm priority photography under auto exposure control including the flashmatic mechanism, and if a constant guide number is set, it follows that the photographing distance is restricted by the selected diaphragm. A quantity of transmitted light which corresponds to the subject distance is not controlled, resulting in a photo with an improper exposure quantity in some cases.
Further, it is impossible to select an emission timing of emitted light.